The present invention relates generally to improvements in particulate control systems and, more particularly, to improvements in particulate control systems that incorporate electrostatic precipitators.
U.S. Pat. Nos. 5,591,253 and 5,683,494 disclose the use of electrostatically enhanced separators (EES) for separating particles from gas streams. Specifically, these patents disclose the use of an EES in conjunction with collectors such as cyclone collectors, bag filters and electrostatic precipitators. However, these patents only disclose the use of an EES in series or in a common loop with other mechanical or electrostatic separators.
Electrostatic precipitators (ESPs) and other collectors are commonly used in electric power generating stations. It has been found that high-resistivity ash produced by burning low-sulfur coals reduces the particulate collection efficiency of electrostatic precipitators (ESPs and other collectors as well). As a result, there is a demand by utilities for low cost improvements to particulate control systems utilizing electrostatic precipitators.
The present invention satisfies the aforenoted needs by providing an apparatus for separating particles from a gas stream that comprises an input line connected to a collector as well as a separator. The collector may be an electrostatic precipitator, cyclone collector, bag filter or other suitable collecting device. The separator may be an electrostatically enhanced separator or other suitable separating device. Downstream of the collector, the collector is connected to a flow distribution valve such as a splitter valve or divider valve. The flow distribution valve connects the collector to an outlet line and a return line. The return line connects the flow distribution valve to the separator so that a portion of the outlet from the collector is returned to the separator. The flow distribution valve divides the output stream from the collector into first and second portions whereby the first portion flows through the outlet line and the second portion flows through the return line to the separator.
In an embodiment, the collector comprises at least one electrostatic precipitator.
In an embodiment, the separator comprises at least one electrostatically enhanced separator as described in U.S. Pat. Nos. 5,591,253 and 5,683,494.
In an embodiment, the apparatus further comprises a second flow distribution valve disposed upstream of both the collector and the separator. The second flow distribution valve connects the input line to the collector and the separator. The second flow distribution valve divides the gas stream into a third portion flowing to the collector and a fourth portion flowing to the separator.
In an embodiment, the apparatus further comprises a bleed line that connects the separator to the collector so that at least a portion of the flow through the separator is directed to the collector.
In an embodiment, the apparatus of the present invention comprises an input line connected to a first flow distribution valve that connects the input line to a first inlet line and a second inlet line. The first inlet line connects the first flow distribution valve to a collector. The second inlet line connects the first flow distribution valve to a separator. The collector is connected to a second flow distribution valve disposed downstream thereof. The second flow distribution valve connects the collector to a first outlet line and a return line. The return line connects the second flow distribution valve to the second inlet line. The second flow distribution valve divides a first output stream from the collector into first and second portions whereby the first portion flows through the first outlet line and the second portion flows through the return line to the second inlet line and to the separator. The first flow distribution valve divides the input gas stream into a third portion flowing through the first inlet line to the collector and a fourth portion flowing through the second inlet line to the separator.
In an embodiment, the present invention provides a method for separating particles from a gas stream which comprises the steps of delivering at least part of the gas stream to a collector, dividing an output from the collector into first and second portions, delivering one of the first and second portions to a separator.
In an embodiment, the method of the present invention further comprises the steps of dividing the gas stream into third and fourth portions upstream of both the collector and the separator and delivering one of the third and fourth portions to the separator and the other of the third and fourth portions to the collector.
In an embodiment, the method further comprises the steps of bleeding a fifth portion of a flow through the separator and delivering the fifth portion to the collector.
In an embodiment, the present invention provides a method for improving the efficiency of a system for separating particles from a gas stream which includes a collector such as an electrostatic precipitator. The method comprises the steps of installing a first splitter valve downstream of the collector, connecting the first splitter valve to a separator such as an electrostatically enhanced separator and a first outlet line so that the first splitter valve is connected to the collector, the first outlet line and the separator, and dividing an output from the collector so that a first portion flows to the first outlet line and a second portion flows to the separator.
In an embodiment, the method further comprises the steps of installing a second splitter valve upstream of the collector and the separator, connecting the second splitter valve to the collector and the separator and dividing the gas stream with the second splitter valve so that a third portion flows to the collector and a fourth portion flows to the separator.
In an embodiment, the method of the present invention further comprises the steps of installing a bleed line connecting the separator to a point upstream of the collector so that a bleed flow will flow from the separator to the collector.
Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments and from the drawings.